There is an increasing demand for tunable lasers for test and measurement uses, wavelength characterization of optical components, fiberoptic networks and other applications. In dense wavelength division multiplexing (DWDM) fiberoptic systems, multiple separate data streams propagate concurrently in a single optical fiber, with each data stream created by the modulated output of a laser at a specific channel frequency or wavelength. Presently, channel separations of approximately 0.4 nanometers in wavelength, or about 50 GHz are achievable, which allows up to 128 channels to be carried by a single fiber within the bandwidth range of currently available fibers and fiber amplifiers. Greater bandwidth requirements will likely result in smaller channel separation in the future.
DWDM systems have largely been based on distributed feedback (DFB) lasers operating with a reference etalon associated in a feedback control loop, with the reference etalon defining the ITU wavelength grid. Statistical variation associated with the manufacture of individual DFB lasers results in a distribution of channel center wavelengths across the wavelength grid, and thus individual DFB transmitters are usable only for a single channel or a small number of adjacent channels.
Continuously tunable external cavity lasers have been developed to overcome the limitations of individual DFB devices. Various laser tuning mechanisms have been developed to provide external cavity wavelength selection, such as mechanically tuned gratings used in transmission and reflection. External cavity lasers must be able to provide a stable, single mode output at selectable wavelengths while effectively suppress lasing associated with external cavity modes that are within the gain bandwidth of the cavity. These goals have been difficult to achieve, and there is accordingly a need for an external cavity laser that provides stable, single mode operation at selectable wavelengths.
Temperature control of emitter chips may be employed in laser devices cool the emitter chips during laser operation. Prior art diode or emitter chip carriers have not been configured for effective heat transfer between the chip and a thermal control source such as a thermoelectric controller or TEC to maintain the chip at an optimal temperature. Typically, the carriers used have a generally square or rectangular shape, with the diode chip mounted on the top of the block-shaped carrier. This type of chip carrier system results in many shortcomings. For example, the square/rectangular shape of the carrier has poor thermal control properties. Particularly, a simple rectangular carrier provides poor heat flow properties, with heat flows occurring primarily in a vertical direction, thus limiting the ability of the rectangular carrier to dissipate heat. As a result of poor heat flow, localized heating on the upper surface of the carrier may occur, which may interfere with the thermal control of the diode chip during and after operation. Diode chips are subject to temperature control during operation to maintain a desired output, and if a desired temperature cannot be maintained, desired output may not be achieved.
Additionally, a simple rectangular carrier can physically hinder the close placement of collimating lenses to the diode chip, therefore requiring the collimating lenses to be positioned at a distance from the diode chip. Positing the collimating lenses further away to accommodate the carrier results in an overall increase of the size of the external cavity diode laser (ECDL), which is undesirable in many applications. Narrowing the width of the carrier to allow closer positioning of the collimating lenses to the diode can overcome this problem. This approach, however, creates a further problem of restricting the thermal conduction path to the heatsink and exacerbates the thermal control problem. In addition, it creates a carrier that may be easily tipped over during assembly (before it is bonded to the TEC or other substrate), therefore making it difficult to handle during assembly. This leads to additional care needed in handling the narrow carrier during assembly, which then leads to increased manufacturing costs of the laser.
Therefore there is a need for a carrier that provides good heat transfer capabilities, that allows the collimating lenses to be placed close to the diode to provide a compact and efficient overall package, and which is easy to handle during manufacturing and assembly. The present invention satisfies these needs, as well as others, and overcomes the deficiencies found in the prior art.